The purpose of the proposed work is to develop the methodology to quantitate the inhomogeneities in the magnitude and rate of change of intramyocardial extracellular potassium activity following acute ligation of the left anterior descending coronary artery in the swine. To do so, we will utilize valinomycin-polyvinyl chloride matriz membrane electrodes developed in our laboratory. The electrodes are uniquely potassium specific. They have a tip diameter of less than 0.5 mm, a time constant of less than 50 msec and exhibit a Nernstian response to changes in potassium activity. Prior studies in our laboratory have established that the changes in potassium activity accurrately mirror changes in myocardial blood flow and are paralleled by changes in ventricular activation. Up to 17 transmural electrodes, each capable of recording potassium activity from the subepicardium, the midmyocardium and the subendocardium will be placed so as to extend from the center to the margin of the ischemic zone. By computer processing the recorded signals, we hope to be able to display graphically the changes in potassium and to determine the variance in the potassium values at 15 second intervals following the occlusion. By so doing, we hope to be able to quantitate the inhomogeneity of the ischemic process as a function of time and to identify the site(s) of greatest inhomogeneity. It is our hypothesis that the inhomogeneities are a critical factor in the genesis of ventricular arrhythmias induced by acute ischemia, and that agents which alter these inhomogeneities will alter the propensity for the arrhythmias. The development of the methodology outlined in this proposal will allow us to test these hypotheses.